This application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in German Patent Application No. 101 14 327.3 filed on Mar. 23, 2001 in the name of Danfoss Compressors GmbH.
The invention relates to a suction muffler for a hermetically enclosed compressor, with a housing having a first part with an outlet channel and a second part with an inlet channel, flow conducting means being arranged between the outlet channel and the inlet channel, said means forming, together with the inlet channel and the outlet channel, a flow path, and a filter being arranged in the outlet channel.
A suction muffler of this kind is known from DE 199 23 734 A1.
Such suction mufflers are preferably used in hermetically enclosed small refrigeration machines, for example like those used in domestic refrigerators and freezers. Such appliances are usually placed in the kitchen or another room in an apartment. They are supposed to work as silently as possible, in order not to interfere with the comfort of an occupant. Therefore, flow conducting means are used to form a flow path for the gaseous refrigerant between an inlet and an outlet chamber. The flow path is shaped so that the movement of the refrigerant generates as little noise as possible. In the prior art, the flow conducting means divides a housing having a first part with the outlet chamber and a second part with the inlet chamber into two chambers, the gas reserves in the chamber connected with the outlet channel have a buffer function, whereas the inlet-side chamber provides an oil trap, meaning that oil gathering here contributes to the noise damping.
Additional suction mufflers are known from U.S. Pat. Nos. 4,911,619 A, 5,252,035 A, EP 0 386 320 A1 or EP 1 031 728 A1. In all cases, a filter is arranged in the suction muffler, the main task of this filter being the removal of oil and impurities contained in the suction gas, to prevent damage to the compression unit.
Based on the foregoing, it is the general object of the present invention to further improve noise damping.
With a suction muffler as mentioned in the introduction, this task is solved in that the filter has a sieve-like embodiment and that the flow path comprises at least one second filter also with a sieve-like embodiment.
The sieve-like embodiment of the filter means that the filter includes a screen of a relatively fine mesh, through which the suction gas flows. The screen can be made of metal wire or fibres or, of corresponding fibres of another material, for example plastic. The embodiment of the filter as a screen or a sieve has two effects.
First, the first filter, as in the known case, serves the purpose of retaining impurities which might damage the compressor if allowed to enter the compression chamber. Of course, also a certain oil separation effect is achieved, which is desired to prevent a high external oil circulation in the refrigerant circuit. It is desirable to retain as much oil as possible in the compressor to lubricate and cool the moving parts thereof. However, the high gas speed in this area only permits oil separation to a limited extent. If oil is still contained in the refrigerant flow, it will be entrained through the sieve. Secondly, however, the sieve-like embodiment of the filter has a substantial noise-damping effect. A noise damping through the first filter is primarily achieved in that the acoustic energy flow coming from the primary acoustic source, namely the valve system, is decreased by the reduction of the free cross-section in the outlet channel. However, a particularly effective noise damping is achieved due to the fact that a second filter, also with a sieve-like embodiment, is arranged in the suction gas flow. In principle, the second filter has a corresponding effect, as a dirt filter, as an oil separator and, in noise damping. However, the major advantage of the second filter is that it damps a second acoustic source inside the suction muffler. The second acoustic source generates noise caused by the refrigerant flow. The cooperation of the two sieves or screens ensures a noise damping which exceeds a pure doubling of the effect of one filter. The oil separation itself basically only requires one filter. The second filter (seen in the flow direction) also separates oil, however, the cooperation of the two filters with their sieve-like embodiment is particularly effective when it comes to noise damping.
It is preferred that the second filter be arranged in a section of the flow path which has one of the smallest effective flow cross-sections. In this section, the suction gas flow then has the highest speed. Channels with a relatively small diameter are passed by a turbulent refrigerant flow. The eddies thus appearing on the surfaces of the channel may cause the channel walls to oscillate, so that they emit acoustic waves. The sieve-like second filter changes the turbulent flow conditions on these surfaces in that it interrupts the turbulent eddy pattern. A vibration of the channel walls is thus minimised or prevented. This is particularly effective in such parts of the flow path which have a relatively small flow cross-section. The effective flow cross-section corresponds to the part of the channel cross-section through which the major part of the refrigerant mass flows.
Preferably, the second filter is allocated to a channel, whose end section is directed towards the first filter. A gas flow is thus generated which is directed towards the first filter. In this gas flow, however, turbulence and pressure waves are substantially damped. In the distance between the outlet of the channel and the first filter, only a small possibility remains for a renewed generation of pressure waves in the suction gas. However, such pressure waves are additionally weakened in the first filter.
Preferably, an insert is arranged in the housing, which separates an upper chamber from a lower chamber and which has a channel between the first chamber and the second chamber, the second filter being allocated to the channel. The formation of an insert in the housing is known per se from DE 199 23 734 A1. Additionally, the second filter is now provided on the tube part, which forms the channel through the insert. This channel is aligned with the outlet channel and the filter at the inlet of the outlet channel. With this embodiment, a sound damping has proved to be particularly effective.
Preferably, at least one filter is arranged on a front side of a channel. This facilitates manufacturing. The filter merely has to be placed on the front side of the channel and connected with the housing part adopting the channel.
It is particularly preferred that in the flow direction the front side is arranged on the inlet side. Through the directional change of the refrigerant flow in the end section of an inlet channel of the suction muffler, an effective flow cross-section occurs at the inlet of the channel, which is smaller than the geometrical cross-section of the channel. In a manner of speaking, the gas is xe2x80x9cpushed to one sidexe2x80x9d.
Therefore, it is particularly advantageous that the second filter is arranged on this front side of the channel facing the inlet. Firstly, here the effective flow cross-section is smallest; secondly turbulence in the complete subsequent channel section is damped. The filter is thus more effective at the channel inlet than it would have been at the channel outlet.
It is particularly preferred that the front side of the channel projects from the housing part, which defines the channel. This simplifies the manufacturing process. When projecting from the housing part, the front side is accessible from all sides. Particularly when automatic handling equipment is used in production, a technical advantage in respect to handling is obtained.
Preferably, the filter is adhered or welded onto a part holding it. This is a very simple production technique which requires no additional parts to fix the filter on the corresponding housing part.
It is also preferred that the first filter is arranged under an angle in relation to the front side of the outlet channel and the second filter is arranged in parallel to the front side of the channel. The different inclinations of the filters to their individual, connected flow channels cause an improved noise damping. Particularly the first filter can work with an improved oil separation effect.
Preferably, a third filter with a sieve-like embodiment is arranged in the flow path.